Converting back to 4.0

Does anyone know how to convert PAF 5.0 back to 4.0.I exported a GEDCOM and made a back up disc.Tried to reinstall 4.0 and import the 5.0 GEDCOM, but it won't let me.Won't let me restore from back up 5.0 to 4.0 either.I am very unhappy with 5.0 and would love to go back to 4.0